1. Field of the Invention
The present invention relates to a pressure relief valve and more particularly to a pressure relief valve having a reduced blow down pressure of about 5% or less and further having an outlet port which is adjustable 360xc2x0 about the relief valve. The relief valve also has a pressure energized seal.
2. Description of the Prior Art
Relief valves are placed in piping systems, pressure vessels and other systems to vent excess pressure from the system in an attempt to prevent damage to the system without endangering the workers or environment. In a relief valve, the pressure at which the valve opens, known as the set pressure, is a function of the spring rate and the initial friction of the seals. The pressure at which the valve closes is also dependent on the set pressure and the stick friction of the seals. Typically, the larger the stick friction component, the lower the system pressure must fall to allow the relief valve to close. The amount the pressure must fall below the set point to allow the relief valve to close is called xe2x80x9cblow downxe2x80x9d.
Blow down is typically expressed as a percentage of the set point (also known as set pressure). For example, if the set point is 4,000 psi, and the blow down dead band is 20%, the pressure within the system must fall to approximately 3,200 psi before the relief valve will close and reseat. High blow down in this type of relief valve is undesirable.
Prior art relief valves typically have a blow down of approximately 15-30%. For example, if the set pressure is 4,000 psi, the pressure must drop to 2800 to 3400 psi before the opened valve reseats. The 1200-600 psi pressure drop represents 30-15% of the set pressure.
Various types of relief valves are known in the art such as those disclosed in the following U.S. Pat. Nos.: 5,168,895; 4,790,348; 4,530,373; 4,313,463; 4,284,101 and 3,232,314. Copies of these patents are included in the Information Disclosure Statement filed concurrently herewith.
A commercially successful relief valve is the subject of U.S. Pat. No. 4,456,028 issued in 1984 and assigned to Gilmore Valve Co., the assignee of the present invention. In order for this relief valve to close, a metal seal disk must slide across a metal sealing surface into sealing engagement with the valve outlet bore. This metal to metal sealing assembly causes friction, resulting in a blow down of approximately 20%. It would be desirable from a systems standpoint to reduce the blow down of the relief valve.
Prior art relief valves further typically include a predetermined outlet port position. At best, the position of the prior art outlets could be changed by disassembly and reconstruction of the valve. A relief valve having an outlet port that is easily and variably positioned without disassembling the valve is desirable. Such a valve is user friendly and easy to install. The present invention has an outlet port that is adjustable 360xc2x0 about the relief valve.
A relief valve is disclosed that performs with blow down values of about 5% or less. This is accomplished by reducing the friction experienced by the relief valve during closing. The relief valve includes a body which houses a plunger that comes into sealing contact with the valve inlet. Clearance is provided between the body and the plunger, thereby eliminating friction on the plunger as it moves into sealing contact with the seal assembly. An energized seal assembly forms a tight seal against the plunger while creating little friction.
The relief valve further includes an outlet port, which is adjustable 360xc2x0 about the valve. An adapter block that defines the relief valve outlet port includes an annular portion that surrounds and is freely rotatable about the valve and a projecting portion that defines the valve outlet port. The adapter block rotates upon o-rings that create a seal as well as providing a sliding surface for the adapter block. The adjustable position outlet port greatly improves the ease of installation of the relief valve.